Many ophthalmic surgical procedures require illuminating a portion of a patient's eye so that a surgeon can observe the surgical site. Various different types of instruments are known and available for use by an ophthalmic surgeon to illuminate the interior of the eye. Ophthalmic illuminators are commonly used for this purpose.
Ophthalmic illuminators allow a surgeon to illuminate the interior structure of the eye, such as the vitreous and the retina, during surgical procedures. The handheld (probe) portion of a typical ophthalmic illuminator comprises a handle having a projecting tip and a length of optical fiber that enters a proximal end of the handle and passes through the handle and the tip to a distal end of the tip, from which light traveling along the optical fiber can project. The proximal end of the optical fiber can be optically coupled to a light source to receive the light that is transmitted through the fiber. Illuminator probes of this type are typically used by inserting the probe tip through a small incision in the eye. In this way, light from the illuminator light source is carried along the optical fiber, through the handpiece and emitted from the distal end of the probe (fiber) to illuminate the surgical site for the surgeon. In addition to the handheld probe and the light source, a typical ophthalmic illumination system further comprises an enclosure to house the light source and associated optics that guide light from the light source to the optical fiber of the probe, a power supply, electronics with signal processing, and associated connectors, displays and other interfaces as known to those having skill in the art.
Modern small-incision techniques require endo-illuminator probes to have a relatively high-gauge cannula, such as 20 gauge (0.0295 inch diameter) or even higher gauges such as 25 gauge. However, surgeons also require sufficient luminous power from the endo-illuminator to properly illuminate the surgical field within the eye. This is not an issue when a highly luminous source, such as prior art tungsten filament, halogen, and/or high-intensity discharge (HID) bulbs, such as metal halide and xenon bulbs, is used as the endo-illuminator light source because the fraction of the light output from such relatively powerful sources coupled to the fiber is of sufficient luminous power to satisfactorily illuminate a surgical field. But such conventional non-solid-state light sources have many drawbacks when used in an ophthalmic illuminator.
For example, these light sources typically have a short useful lifetime. Because the bulbs and lamps burn out every 300-400 hours, there is a good chance they may burn out during a surgical procedure. Thus, such failures increase the risk of harm to the patient because of the immediate lack of light and the interruption of surgery. The bulb replacement cost is also very high in current ophthalmic endo-illuminators.
Furthermore, these prior art bulbs and lamps generate substantial amounts of heat while consuming substantial amounts of power such that current ophthalmic endo-illuminators have to be made of components capable of withstanding high temperature. Because of the heat produced by the bulbs and lamps used in current ophthalmic illuminators, a cooling fan is typically implemented within the illuminator, which adds to the cost of production/use as well as increases the bulkiness/size of the illuminator. This fan also generates substantial levels of noise in the operating room. In use, these bulbs and lamps take a certain time period to warm up (e.g. tungsten filament to reach thermal equilibrium) during which the color and brightness produced by the ophthalmic illuminator changes.
In contrast, an LED source for an endo-illuminator is much cooler and consumes less power, making it more suitable for use in an operating room environment and, for example, for battery-powered applications. Moreover, an LED source is safer as LEDs are less prone to burning out during surgical procedures as compared to conventional bulb sources. In addition, LEDs are less costly as compared to halogen or HID sources. Although LED light sources thus make an attractive alternative to the conventional use of HID or halogen bulbs, their luminance is typically less than a conventional bulb source. Thus, due to the relatively high etendue of a conventional LED and its relatively low luminance, a conventional LED light source, and particularly single LED light sources, will not pass sufficient light energy into a low etendue optical fiber.
Known methods for attempting to increase the luminance of an LED light source beyond that of a single LED suffer from configuration problems, limited luminance improvement and non-uniformity of the provided light output. For example, one attempt at a solution involves arranging LED's into a cubic shaped configuration with an output aperture at the top of the cube. However, due the constraints imposed by the LED substrate (e.g., thermal management requires a minimum distance between the LED chips) it is not possible to arrange the LED chips close enough to one another to provide a combined output luminance greater than that of a single LED chip. FIG. 2 is a diagrammatical representation of such a prior art arrangement.
Other similar attempted solutions are known. For example, U.S. Pat. Nos. 6,960,872 and 7,025,464 describe high luminance LED scatter boxes comprising multiple LEDs arranged inside of a box, the interior coated with high reflectance diffusive material, and the box having an exit port for the combined LED output light. The described approaches have exit ports having a reduced area compared to the emitting area of the individual LEDs. While the resulting devices may be capable of increased luminance over that of a single LED, the less than 100% reflectance of the diffuse reflective surface of the inside of the scatterbox limits the amount of luminance improvement possible. Further, some view angles looking back into the scatterbox through the exit port will orient directly at an LED-emitting surface, which has a higher luminance than that of the diffuse surface of the box adjoining the LED. The resultant angular luminance non-uniformities of the light emitted from the exit port are not desirable in certain applications, such as for illumination of ophthalmic procedures.
Therefore, a need exists for a method and system for enhanced LED ophthalmic illumination that can reduce or eliminate the problems of prior art ophthalmic illumination systems discussed above, including increasing the luminance of an LED light source to provide sufficient luminous power to a surgical site without increasing the LED current, which typically would result in more dissipated electrical power and more problematic thermal management issues.